Embedded Bio-Sensor System

ABSTRACT

Provided is a bio-sensor system which utilizes radio frequency identification technology and which includes a remote transponder in wireless communication with an implantable passively-powered on-chip transponder. The bio-sensor system is specifically adapted to provide a substantially stable and precise sensor reference voltage to a sensor assembly that is included with the on-chip transponder. The remote transponder is also configured to remotely receive data representative of a physiological parameter of the patient as well as identification data and may enable readout of one or more of the physiological parameters that are measured, processed and transmitted by the on-chip transponder upon request by the remote transponder. The precision and stability of the sensor reference voltage is enhanced by the specific circuit architecture of the glucose sensor to allow for relatively accurate measurement of the physiological parameter such as measurement of glucose concentration by a glucose sensor without the use of a microprocessor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/582,790, filed on Oct. 18, 2006, which is a continuation ofU.S. application Ser. No. 10/849,614, filed on May 20, 2004, whichissued as U.S. Pat. No. 7,125,382 on Oct. 24, 2006, all of which areincorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

The present invention relates to sensor devices and, more particularly,to an bio-sensor system configured for wirelessly transmitting data to aremote transponder from an on-chip transponder having a sensor and whichis implantable in a patient. The bio-sensor system is specificallyadapted to apply a stable and precise voltage to an electrode system ofthe sensor such that glucose concentration levels of the patient may beaccurately measured.

The blood glucose concentration level of a patient is normallycontrolled by the pancreas. However, for patients suffering fromdiabetes, the pancreas does not properly regulate the production ofinsulin needed to metabolize food into energy for the individual. Fordiabetic patients, glucose levels must be checked or monitored severaltimes throughout the day so that insulin may be periodicallyadministered in order to maintain the glucose concentration at a normallevel. In one popular method, the glucose level is monitored by firstobtaining a sample of blood from finger-pricking. The glucose level ofthe blood sample is then placed on a glucose measurement strip and asubsequent chemical reaction produces a color change that may becompared to a reference chart. In this manner, the reaction of the bloodsample with the glucose measurement strip provides an indication as towhether the glucose level is abnormally low or high such that thediabetic patient may administer the proper amount of insulin in order tomaintain the glucose concentration within a predetermined range. Suchadministration of insulin is typically performed by way ofself-injection with a syringe.

Unfortunately, the finger-pricking method of glucose testing isuncomfortable as both the blood-pricking and the insulin injections arepainful and time-consuming such that many diabetic patients arereluctant to check their glucose levels at regular intervals throughoutthe day. Unfortunately, glucose levels often fluctuate throughout theday. Therefore, even diabetic patients who are otherwise consistent inchecking their glucose levels at regular intervals throughout the daymay be unaware of periods wherein their glucose levels are dangerouslylow or high. Furthermore, the finger-pricking method is dependent onpatient skill for accurate testing such that the patient may rely onerroneous data in determining the dosage level of insulin. Finally,self-monitoring of glucose levels imposes a significant burden on lesscapable individuals such as the young, the elderly and thementally-challenged.

At the time of this writing, it is estimated that 17 million people inthe United States, or about six percent of the population, havediabetes. Due in part to dietary habits and an increasingly sedentarylifestyle, particularly among children, diabetes is expected to increaseat the rate of about 7 percent every year such that the disease ispredicted to eventually reach epidemic proportions. In addition, thecurrent cost of diabetes in the United States alone is estimated at over$120 billion with the total U.S. sales of the glucose measuring stripsalone estimated at about $2 billion. Thus, there is a demand forcontinuous, reliable and low-cost monitoring of glucose levels ofdiabetic patients due to the increasing number of people diagnosed withdiabetes.

Included in the prior art are several implantable devices have beendeveloped in an effort to provide a system for continuous and reliableglucose monitoring. In such implantable devices, an electrochemicalsensor is embedded beneath the skin of the patient. The electrochemicalsensor detects the glucose concentration level and transmits signalsrepresentative of the glucose concentration level to a receiving device.Unfortunately, such implantable devices suffer from severaldeficiencies. One such deficiency is that implantable devices may expenda substantial amount of power in sensing and processing bio-signals. Thepower requirement for such devices necessitates the use of largebatteries in order to prolong the useful life. Unfortunately,implantable devices having batteries as the power source may requireperiodic surgeries for replacement of the batteries when the capacitydrops below a minimum level.

Furthermore, some batteries contain materials that may present a risk ofharm to the patient due to toxic substances or chemical within thebattery that may leak into the patient after implantation. Also, due tothe relatively limited power capacity of batteries, the range offunctions that may be performed by the implantable device may besomewhat limited. Finally, it may be desirable to monitor multiplephysiological parameters in addition to glucose concentration levels. Insuch cases, the implantable device may require multiple sensors whereineach sensor simultaneously monitors a different physiological parameterof the patient. For example, in addition to monitoring glucoseconcentration levels, the temperature and heart rate of the patient mayalso be monitored. Such an implantable device having multiple sensorsmay consume more power than can be supplied by a battery that isminiaturized for use in an implantable device.

One implantable device in the prior art overcomes the above noteddeficiency associated with large power requirements by providing abio-sensor system that is passively powered such that the operating lifeof the bio-sensor is theoretically unlimited. As understood, thepassively powered bio-sensor system includes at least one sensor that isimplanted in a patient. The implanted sensor monitors physiologicalconditions of the patient. An implanted passive transponder receives thesensor signals from the sensor, digitizes the sensor signals andtransmits the digitized sensor signal out of the patient's body whensubjected to an interrogation signal from a remote interrogator. Theinterrogator also energizes the implanted transponder such that thebio-sensor system may be passively powered. In this manner, thepassively powered bio-sensor system requires no batteries such that itessentially has an unlimited operating life.

Another deficiency of implantable devices pertains to electrochemicalsensors that are utilized therein to measure glucose concentrationlevels in the patient's blood. Such sensors typically use anamperometric detection method wherein oxidation or reduction of acompound is measured at a working electrode in order to determinesubstance concentration levels. A potentiostat is used to apply aconstant potential or excitation voltage to the working electrode withrespect to a reference electrode. In measuring glucose concentrationlevels in the blood, glucose oxidase (GOX) is typically used as acatalyst to oxidize glucose and form gluconic acid, leaving behind twoelectrons and two protons and reducing the GOX. Oxygen that is dissolvedin the patient's blood then reacts with GOX by accepting the twoelectrons and two protons to form hydrogen peroxide (H₂O₂) andregenerating oxidized GOX.

The cycle repeats as the regenerated GOX reacts once again with glucose.The consumption of O₂ or the formation of H₂O₂ is subsequently measuredat the working electrode which is typically a platinum electrode. Asoxidation occurs at the working electrode, reduction also occurs at thereference electrode which is typically a silver/silver chlorideelectrode. The more oxygen that is consumed, the greater the amount ofglucose in the patient's blood. In the same reaction, the rate at whichH₂O₂ is produced is also indicative of the glucose concentration levelin the patient's blood. Because the potentiostat controls the voltagedifference between the working electrode and the reference electrode,the accuracy with which the sensor measures glucose concentration levelsis dependent on the accuracy with which the voltage is applied. If thevoltage that is applied to the sensor is excessive, the silver or silverchloride reference electrode may be excessively consumed such that thereference electrode may become damaged. Furthermore, erroneousmeasurements of glucose concentration levels may result such that theability of the patient to administer insulin in order to correct forabnormalities in glucose concentration levels may be compromised

In an attempt to overcome the above-described deficiency associated withtwo-electrode electrochemical sensors, three-electrode electrochemicalsensors have been developed wherein an auxiliary electrode is includedwith the working electrode and the reference electrode. The inclusion ofthe auxiliary electrode is understood to reduce the consumption ofsilver and silver chloride by reducing the magnitude of current flowingthrough the reference electrode, thereby stabilizing the electrodepotential. Unfortunately, such three-electrode electrochemical sensorsof the type describe above add complexity and cost to the bio-sensorsystem due to the increased difficulty in manufacturing and operatingsuch electrochemical sensors.

As can be seen, there is a need for an implantable bio-sensor systemthat overcomes the above-described deficiencies associated with thestability of the reference electrode potential with respect to theworking electrode. More specifically, there exists a need in the art foran implantable bio-sensor system that provides a stable and accuratevoltage to the electrochemical sensor in order to improve the accuracywith which glucose concentration levels may be measured. In combinationwith the power requirements, there is also a need in the art for animplantable bio-sensor system that enables the simultaneous andselective monitoring of multiple physiological parameters of the patientthrough the use of multiple bio-sensors included with the implantabledevice. Furthermore, there exists a need in the art for an implantablebio-sensor system which allows full-duplex operation such that requestsfor data (i.e., physiological parameters of the patient) andtransmission of such data can be simultaneously performed. Finally,there is a need in the art for an implantable bio-sensor system thatenables continuous readout of the data at a remote device.

BRIEF SUMMARY OF THE INVENTION

Provided is a telemetric bio-sensor system which utilizes radiofrequency identification (RFID) technology and which includes a remotetransponder that is in wireless communication with a passively poweredon-chip transponder. The bio-sensor system is specifically adapted toprovide a substantially stable and precise voltage to a sensor assemblythat is included with an implantable on-chip transponder. The remotetransponder is placed within a predetermined distance of the on-chiptransponder in order to supply power to and request telemetry data fromthe on-chip transponder. The remote transponder is also configured toremotely receive data representative of a physiological parameter of thepatient as well as identification data and may enable readout of one ormore of the physiological parameters that are measured, processed andtransmitted by the on-chip transponder upon request by the remotetransponder.

Importantly, the power receiver supplies a substantially non-deviatingsensor reference voltage to the sensor in order to enhance the accuracywith which the physiological parameter is measured. The precision andstability of the sensor reference voltage (i.e., the sensor power) isenhanced by the specific circuit architecture of the glucose sensor. Theapplication of the substantially stable voltage to the sensor assemblyallows for relatively accurate measurement of the physiologicalparameter of the patient such as measurement of a glucose concentrationlevel by a glucose sensor. The technique of generating the stable andprecise voltage may be applied to a 2-pin glucose sensor as well as to a3-pin glucose sensor without the use of a microprocessor such that costand power consumption of the on-chip transponder may be reduced.Advantageously, the stability and accuracy of the sensor referencevoltage is achieved without the use of a microprocessor to reduce powerconsumption of the on-chip transponder as well as reduce overall costsof the bio-sensor system.

The on-chip transponder includes the sensor assembly having the sensorwhich may be the 2-pin or 3-pin glucose sensor. However, any othersensor may be used with the on-chip transponder. Components of theon-chip transponder may include: the sensor, a power receiver, ananalog-to-digital (A/D) assembly, a data processor and an RF transmitterwhich may preferably be interconnected using conventional integratedcircuit technology such that the on-chip transponder may be packagedinto a sufficiently small size for implantation into a patient. An RFreceiver may also be included with the on-chip transponder to allow forselection among a plurality of sensors and to allow for full-duplexing,which enables continuous and/or simultaneous two-way wirelesscommunication between the remote transponder and the on-chiptransponder.

The remote transponder emits a scanner signal that is received by apower receiver of the on-chip transponder. The power receiver convertsthe scanner signal to a power signal to power the A/D assembly, a dataprocessor and an RF transmitter. The A/D assembly converts thephysiological parameter contained in an analog electrical signal comingfrom the sensor into digital format in a digital signal. The A/Dassembly may also add a unique identification code to the digital signalto identify the particular sensor from which the sensor signaloriginated.

The data processor receives the digital signal from the A/D assembly andfilters, amplifies and/or encodes the digital signal to generate aprocessed data signal. The data processor may also gate the data signalto determine when to transmit the data signal and may also sum the datasignal with other data (i.e., from other sensors). The RF transmitterimpresses (i.e., modulates) the data signal onto a radio carrier of adesired frequency, amplifies the modulated carrier and sends it to anantenna for radiation to the remote transponder.

BRIEF DESCRIPTION OF THE DRAWINGS

These as well as other features of the present invention will becomemore apparent upon reference to the drawings wherein:

FIG. 1 a is a block diagram of a sensor assembly and an on-chiptransponder of an implantable bio-sensor system of the present inventionin an embodiment enabling simplex operation wherein the content andduration of a signal transmitted by the on-chip transponder ispre-programmed;

FIG. 1 b is a block diagram of the sensor assembly and the on-chiptransponder of the bio-sensor system in an embodiment enabling duplexoperation wherein the duration and content of signals transmitted by theon-chip transponder to a remote transponder, and vice versa, isselectable;

FIG. 2 is a block diagram of a remote transponder of the implantablebio-sensor system;

FIG. 3 is a block diagram of a data processor that may be included withthe on-chip transponder;

FIG. 4 is a block diagram of a radio frequency (RF) transmitter that maybe included with the on-chip transponder;

FIG. 5 a is a block diagram of an analog-to-digital (A/D) assembly asmay be included with the on-chip transponder for the embodiment of thebio-sensor system configured to receive a single one of the sensorsignals;

FIG. 5 b is a block diagram of the A/D assembly as may be included withthe on-chip transponder for the embodiment of the bio-sensor system thatmay include a switch for selecting a sensor signal sent from multiplesensors;

FIG. 6 is a block diagram of a power receiver that may be included withthe on-chip transponder;

FIG. 7 is a block diagram of an RF receiver that may be included withthe on-chip transponder;

FIG. 8 a is a schematic representation of a 2-pin glucose sensor as maybe incorporated into the sensor assembly; and

FIG. 8 b is a schematic representation of a 3-pin glucose sensor as maybe incorporated into the sensor assembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein the showings are for purposes ofillustrating various aspects of the invention and not for purposes oflimiting the same, provided is a uniquely configured telemetricbio-sensor system 10 which utilized radio frequency identification(RFID) technology and which includes a remote transponder 800 that is inwireless communication with a passively powered on-chip transponder 100.The bio-sensor system 10 is specifically adapted to provide asubstantially stable and precise voltage to a sensor assembly 200 thatis included with the on-chip transponder 100. The on-chip transponder100 is implantable into a host such as a human patient.

The remote transponder 800, which may be a compact handheld device, maybe manually placed within a predetermined distance (e.g., within severalfeet) of the on-chip transponder 100 in order to supply power to andrequest telemetry data from the on-chip transponder 100. The remotetransponder 800 may alternatively be fixedly mounted and may beconfigured to automatically transmit power and telemetry request data tothe patient and, hence, the on-chip transponder 100 when the patientmoves within the predetermined distance to the remote transponder 800.Regardless of whether it is handheld, fixedly mounted or otherwisesupported, the remote transponder 800 is configured to remotely receivedata representative of a physiological parameter of the patient as wellas identification data such that the data may be stored or displayed.

Importantly, the application of the substantially stable voltage to thesensor assembly 200 allows for relatively accurate measurement of thephysiological parameter of the patient such as measurement of a glucoseconcentration level by a glucose sensor 210. As will be demonstratedbelow, the technique of generating the stable and precise voltage may beapplied to a 2-pin glucose sensor 210 as well as to a 3-pin glucosesensor 210. Importantly, the bio-sensor system 10 provides the stableand precise voltage to the sensor assembly 200 without the use of amicroprocessor such that cost and power consumption of the on-chiptransponder 100 may be reduced.

In its broadest sense, the bio-sensor system 10 and operational methodof use thereof comprises the implantable on-chip transponder 100 and theremote transponder 800 in wireless communication with one another. Asmentioned above, the sensor assembly 200 is connected to or integralwith the on-chip transponder 100 and may be implanted in the patientwith the on-chip transponder 100. The bio-sensor system 10 is configuredsuch that the remote transponder 800 may enable readout of one or moreof the physiological parameters that are measured, processed andtransmitted by the on-chip transponder 100 upon request by the remotetransponder 800. The bio-sensor system 10 may be configured to operatein simplex mode as shown in FIG. 1 a.

Alternatively, the bio-sensor system 10 may be configured to operate induplex mode as shown in FIG. 1 b wherein the on-chip transponder 100additionally includes an intelligent radio frequency (RF) receiver. Whenprovided with the RF receiver 700, the bio-sensor system 10 enablesfeatures such as selection between multiple sensors 210 and/orcontinuous readout of data (e.g., physiological parameters of thepatient) in addition to readout of identification data which may becorrelated to a patient database containing information regarding thepatient's identity as well as information regarding the patient's age,weight, medical history, etc.

Referring more particularly now to FIGS. 1 a and 1 b, shown are blockdiagrams of the sensor assembly 200 as connected to the on-chiptransponder 100 of the bio-sensor system 10 for respective embodimentsenabling simplex and duplex operation. The on-chip transponder 100includes the sensor assembly 200 having the sensor 210. The sensor 210may be configured as the 2-pin glucose sensor 210 or as 3-pin glucosesensor 210 as was mentioned above. However, any other sensor may be usedwith the on-chip transponder 100. For example, the sensor 210 may beconfigured as at least one of the following: a pressure transducer, ablood sugar sensor, a blood oxygen sensor, a heart rate monitor, arespiratory rate sensor, etc. In this regard, the sensor 210 may beconfigured as any type of sensor for measuring, monitoring or detectingany type of physiological parameter of the patient.

Shown in FIG. 2 is a block diagram of the remote transponder 800. Theremote transponder 800 is configured to wirelessly request dataregarding the physiological parameter by transmitting a scanner signal882 to the on-chip transponder 100. The remote transponder 800 is alsoconfigured to receive a data signal 462 representative of thephysiological parameter from the on-chip transponder 100. In the samemanner, the on-chip transponder 100 is configured to communicate withthe remote transponder 800 and receive the scanner signal 882 andtransmit the data signal 462 therefrom once the remote transponder 800and on-chip transponder 100 are within sufficiently close proximity toone another to enable wireless communication therebetween.

Components of the on-chip transponder 100 for the embodiment of thebio-sensor system 10 enabling simplex operation include: the sensor 210,a power receiver 600, an analog-to-digital (A/D) assembly 300, a dataprocessor 400 and an RF transmitter 500, as shown in FIG. 1 a. Forembodiments of the bio-sensor system 10 enabling duplex operation, theRF receiver 700 is included with the on-chip transponder 100, as shownin FIG. 1 b. Each of the components of the on-chip transponder 100 maybe electrically interconnected via conventional conductive wiring.However, electrical connections may preferably be provided usingconventional integrated circuit technology such that the on-chiptransponder 100 may be packaged into a sufficiently small size forimplantation into the patient.

The sensor 210 is configured to generate a sensor signal 234representative of the physiological parameter of the patient and is madeup of a positive signal and a negative signal transmitted in paralleland sent from the sensor 210 to the A/D assembly 300, as shown in FIGS.1 a and 1 b. For embodiments of the bio-sensor system 10 enablingsimplex operation, the power receiver 600 is configured to receive thescanner signal 882 at antenna 601 and to generate a power signal 602 forpassively powering the on-chip transponder 100. For embodiments of thebio-sensor system 10 enabling duplexing, the RF receiver 700 receivesthe scanner signal 882 at antenna 701 for delivery to the power receiver600. The A/D assembly 300 is connected to the power receiver 600 viapower line 604 to receive the power signal 602. The A/D assembly 300 isalso connected to the sensor 210 to receive the analog sensor signal 234therefrom. Once powered by the power signal 602, the A/D assembly 300 isconfigured to generate a digital signal 372 in response to the analogsensor signal 234 coming from the sensor 210.

Referring still to FIGS. 1 a and 1 b, the data processor 400 isconnected to the A/D assembly 300 and the power receiver 600 and isconfigured to receive the power signal 602, via power line 606, as wellas the digital signal 372 from the A/D assembly 300. Upon powering bythe power signal 602, the data processor 400 is configured to generate adata signal 462 in response to the digital signal 372. In general, thedata processor 400 receives the digital signal 372 and filters,amplifies and/or encodes the digital signal 372 to generate the datasignal 462. The data processor 400 may be configured to gate the datasignal 462 to determine when to transmit the data signal 462 to theremote transponder 800. In addition, the data processor 400 may also beconfigured to sum the data signal 462 with other data (i.e., from othersensors 210), as will be explained in greater detail below.

The RF transmitter 500 is connected to the power receiver 600 via powerline 608 to receive the power signal 602. The RF transmitter 500 is alsoconnected to the data processor 400 and is configured to receive thedata signal 462 therefrom. The RF transmitter 500 is also configured tomodulate, amplify, filter and transmit the data signal 462 for receiptback to the remote transponder 800. In general, the RF transmitter 500impresses (i.e., modulates) the data signal 462 onto a radio carrier ofa desired frequency, amplifies the modulated signal and sends themodulated signal to antenna for radiation to the remote transponder 800.

The power receiver 600 circuitry is configured similar to the circuitryof a voltage regulator, as is well known in the art, wherein referencediodes and resistors are arranged in such a manner as to generate anapproximate supply voltage. However, the power receiver 600 is alsospecifically configured to supply a suitable voltage to the sensor 210processing circuitry without delivering substantial current so as toreduce complexity. Thus, in addition to collecting, rectifying,filtering and regulating power for supply to the A/D assembly 300, dataprocessor 400 and RF transmitter 500, the power receiver 600 alsoprovides the substantially stable and precise voltage to the sensorassembly 200.

More specifically, the power receiver 600 is configured to supply asubstantially non-deviating sensor reference voltage signal 642 to thesensor 210 in order to enhance the accuracy with which the physiologicalparameter is measured. The precision and stability of the sensorreference voltage signal 642 (i.e., the sensor 210 power) is enhanced bythe specific circuit architecture of the glucose sensor 210, as is shownin FIGS. 8 a and 8 b and as will be described in greater detail below.In this manner, the accuracy of glucose concentration levels, asrepresented by an output signal from the glucose sensor 210, isimproved. As was earlier mentioned, once the physiological parameter ismeasured by the sensor 210, the remote transponder 800 is configured toreceive the data signal 462 from the RF transmitter 500 and extract datarepresentative of the physiological parameter for storage and/ordisplay.

For embodiments of the bio-sensor system 10 enabling duplex operation,the on-chip transponder 100 additionally includes the RF receiver 700which is configured to receive the scanner signal 882 from the remotetransponder 800, as shown in FIG. 1 b. In a broadest sense, the scannersignal 882 is received at antenna 701 and is decoded by the RF receiver700 to inform the on-chip transponder 100, via a message signal 702,that a request for data has been made. The power receiver 600 alsoconverts the scanner signal 882 into the power signal 602 for relay tothe A/D assembly 300, the data processor 400 and the RF transmitter 500via respective ones of the power lines 604, 606, 608, as was describedabove. The RF receiver 700 is configured to filter, amplify anddemodulate the scanner signal 882 and generate the message signal 702for delivery to controlling components of the on-chip transponder 100.More specifically, the message signal 702 is transmitted to the A/Dassembly 300, the data processor 400 and the RF transmitter 500 viarespective ones of the message/control lines 704, 706, 708, as shown inFIG. 1 b. The RF receiver 700 may be in two-way communication with theA/D assembly 300, the data processor 400 and the RF transmitter 500 viarespective ones of the message/control lines 704, 706, 708 through whichthe message signal 702 may be transmitted.

For configurations of the bio-sensor system 10 having a plurality ofsensors 210, each one of the sensors 210 may be operative to sense adistinct physiological parameter of the patient and generate the sensorsignal 234 representative thereof. For example, an additional one of thesensors 210 may be provided to measure an internal body temperature ofthe patient. Still further, an additional one of the sensors 210 may beprovided to measure a blood pressure level of the patient. The pluralityof sensors 210 may generate a plurality of sensor signals 234. The RFreceiver 700 may be configured to coordinate requests for data from oneor more of the plurality of sensors 210 for subsequent transmission ofthe data back to the remote transponder 800, as will be described ingreater detail below. For embodiments of the bio-sensor system 10 havingmultiple sensors 210, the data processor 400 may be configured to assigna preset identification code to the digital signal 372 for identifyingthe sensor 210 from which the sensor signal 234 originates. In such anembodiment, the A/D assembly 300 may include a switch 310 that isresponsive to the message signal 702 and which is operative to selectamong the plurality of sensor signals 234 for subsequent transmissionthereof.

Referring now to FIGS. 8 a and 8 b, for configurations of the bio-sensorsystem 10 wherein the sensor 210 is a glucose sensor 210 having anelectrode assembly 201, the specific circuit architecture of the glucosesensor 210 is preferably such that the sensor reference voltage signal642 is supplied to the electrode assembly 201 at a substantiallyconstant value of about positive 0.7 volts. Advantageously, thestability and accuracy of the sensor reference voltage signal 642 isachieved without the use of a microprocessor. The circuit architectureincludes an electrode assembly 201 having a first terminal 202 (i.e., aworking electrode) and a second terminal 204 (i.e., a referenceelectrode) that are both placed in fluid communication with thepatient's blood.

The 2-pin glucose sensor 210 may be configured to measure the glucoselevel using glucose oxidase (GOX) as a catalyst to cause oxidation ofglucose in the patient's blood which forms gluconic acid and whichreduces the GOX. Oxygen (O2) in the patient's blood reacts with the GOXto form hydrogen peroxide (H₂O₂) and regenerate the oxidized GOX. Theconsumption of O₂ or the formation of H₂O₂ is measured at the firstterminal 202, which may be fabricated of platinum. While oxidationoccurs at the first terminal 202, reduction is measured at the secondterminal 204, which may be fabricated of silver/silver chloride. Therate at which O₂ is consumed and H₂O₂ is formed is indicative of theglucose concentration level in the patient's blood. Advantageously,supplying the sensor reference voltage signal 642 to the first terminal202 at a substantially constant value of about positive 0.7 increasesthe accuracy with which the glucose concentration level may be measuredby the 2-pin glucose sensor 210 as well as the 3-pin glucose sensor 210.

Referring still to FIG. 8 a, measurement accuracy of glucoseconcentration level by the 2-pin glucose sensor 210 is enhanced by thecircuit architecture thereof. As can be seen, the 2-pin glucose sensor210 includes a first precision resistor 224, a first operationalamplifier 220, a voltmeter 250, a second operational amplifier 230 and atunable second precision resistor 240. The first precision resistor 224is connected to the power receiver 600 and is configured to receive thesensor reference voltage signal 642 therefrom for excitation of theglucose sensor 210. The first operational amplifier 220 is connected tothe first precision resistor 224 through the first signal line 212 andis configured to receive the sensor reference voltage signal 642. Thefirst operational amplifier 220 discharges a precision sensor referencevoltage signal 223 at a non-inverting input 232 thereof in response tothe sensor reference voltage signal 642.

The voltmeter 250 is connected to a non-inverting input of firstoperational amplifier 220 and to the first precision resistor 224 and isconfigured to monitor the precision sensor reference voltage signal 223.The voltmeter 250 is configured to establish a sensor 210 operatingpoint and more accurately interpret responses of the sensor 210. Thevoltmeter 250 also cooperates with non-inverting first operationalamplifier 220 to buffer the precision sensor reference voltage signal223 and apply a substantially accurate sensor reference voltage signal226 to the first terminal 202. The second operational amplifier 230 isconnected to the second terminal 204 through the second signal line 214and is configured to receive current discharging from the secondterminal 204 in response to the accurate sensor reference voltage signal226 applied to the first terminal 202.

The tunable second precision resistor 240 is connected between an outputand an inverting input of the second operational amplifier 230 andcooperates therewith to generate the sensor signal 234 that issubstantially proportional to the glucose level of the patient's blood.The current is delivered to an inverting terminal of the secondoperational amplifier 230 having a non-inverting input 232 which isgrounded, as shown in FIG. 8 a. Accurate current measure (e.g.,discharging from the second terminal 204) at the second operationalamplifier 230 is established by the tunable second precision resistor240. By configuring the glucose sensor 210 in this manner, the need fora microprocessor is eliminated and the associated calibration proceduresand current drain. Output of the second operational amplifier 230 asdetermined by the precision sensor reference voltage 223 as well as bythe sensor 210 operating point (i.e., glucose levels) and the secondprecision resistor 240, is then processed and transmitted upon requestby the remote transponder 800.

Referring briefly to FIG. 8 b, shown is a block diagram of the 3-pinglucose sensor 210 which is similar to the block diagram of the 2-pinglucose sensor 210 shown in FIG. 8 a with the addition of a thirdterminal 206 (i.e., an auxiliary electrode) to the electrode assembly201. The 3-pin glucose sensor 210 also includes an auxiliary controlcircuit 260. The third terminal 206 is co-located with the first andsecond terminals 204, 206 and is also preferably in fluid communicationwith the patient's blood. The auxiliary control circuit 260 is connectedbetween the third terminal 206 and the second operational amplifier 230through the third signal line 216 and is configured to monitor andcontrol an amount of current discharging from the third terminal 206.The third terminal 206 is configured to divert current away from thesecond terminal 204 during application of the accurate sensor referencevoltage signal 226 applied to the first terminal 202. The addition ofthe third terminal 206 to the electrode assembly 201 of the 3-pinglucose sensor 210 may help to reduce the consumption of silver and/orsilver chloride contained in the second terminal 204 by drawing aportion of current away from the second terminal 204. In this manner,the third terminal 206 acts to stabilize the electrode potential and theoperational life of the glucose sensor 210 may be increased.

Referring now to FIGS. 5 a and 5 b, the architecture of the A/D assembly300 will be described in detail. In general, the A/D assembly 300 isconfigured to convert the physiological parameter contained into ananalog electrical signal which may be represented as current or voltage.The A/D assembly 300 may also perform encoding to include messageencryption of the sensor signal 234, the addition of a uniqueidentification code or message (e.g., to identify the particular sensor210(s) from which the sensor signal(s) 234 originated). In addition, theA/D assembly 300 may include error detection and prevention bits withthe sensor signal 234 to ensure the integrity of the sensor signal 234(i.e., to verify that the data sent from the sensor 210 is equivalent tothe data received).

Referring more specifically to FIG. 5 a, shown is a block diagram of theA/D assembly 300 for the embodiment of the bio-sensor system 10configured to receive the sensor signal 234 from a single sensor 210,such as from the glucose sensor 210. FIG. 5 b is a block diagram of theA/D assembly 300 for the embodiment of the bio-sensor system 10additionally including the switch 310 to allow for selection among aplurality of sensor signals 234 sent from a plurality of the sensors210. In FIGS. 5 a and 5 b, common subcomponents of the A/D assembly 300include a processor filter 320, an amplifier 330, a voltage comparator340, an A/D converter 350, a covert logic device 360 and a controller370. The processor filter 320 is connected to the sensor 210 and isconfigured to receive the sensor signal 234 therefrom. The sensor signal234 is characterized by an analog voltage which, in the case of theglucose sensor 210, is substantially proportional to glucoseconcentration. The voltage may or may not have been processed inpreparation for transmission to the remote transponder 800. In any case,further sensor signal 234 preparation may be required.

As shown in FIGS. 5 a and 5 b, the processor filter 320 receives thesensor signal 234 and generates a filtered signal 322 in responsethereto. The processor filter 320 may perform biasing functions as wellas measurement of the sensor 210 status. The processor filter 320 mayalso strip off spectral components (e.g., high frequency noise spikes)from the sensor signal 234 as well as perform normalizing of the voltagelevels to match the capabilities of the on-chip transponder 100.Additional functions may be performed by the processor filter 320 suchas averaging and other functions required to ensure accurate sampling ofthe sensor 210 data.

The amplifier 330 is connected to the processor filter 320 and isconfigured to receive the filtered signal 322 therefrom and amplify thefiltered signal 322 such that a minimum and maximum voltage of thesignal is within the limits of the A/D converter 350 in order to providemaximum resolution of the digitized signal. Upon receiving the filteredsignal 322, the amplifier 330 is configured to generate an amplifiedsignal 332 in response to the filtered signal 322. The voltagecomparator 340 is connected to the power receiver 600 and is configuredto receive the power signal 602 therefrom and generate a normalizedvoltage signal 342 in response thereto. More specifically, the voltagecomparator 340 normalizes the A/D assembly 300 circuitry such that itsoperating conditions match the need of the sensor signal 234 to bedigitized.

The normalized voltage signal 342 is then first sampled and thenquantized by the A/D assembly 300 prior to digitization. This functionis performed by the A/D converter 350 which is connected between theamplifier 330 and the voltage comparator 340. The A/D converter 350 isconfigured to receive the amplified signal 332 and the normalizedvoltage signal 342 and generate a converter signal 352 in responsethereto. A single sample may be collected or multiple samples may becollected in order to provide a more accurate average or to trackvariations in the sensor signal 234 over a period of time (e.g., overseveral heartbeats of the patient within whom the sensor 210 may beimplanted). The covert logic device 360 receives the converter signal352 from the A/D converter 350. The covert logic device 360 is also intwo-way communication with the controller 370 such that the covert logicdevice 360 receives the converter signal 352 and generates a logicsignal 362 in response thereto. The covert logic device 360 may alsocontain error correction and/or voltage level-shift circuitry.

The controller 370 is configured to gate the A/D assembly 300 forsynchronizing signal transmission with the data processor 400. As shownin FIG. 5 a, the controller 370 is in two-way communication with thecovert logic device 360. Referring to FIG. 5 b for the embodiment of thebio-sensor system 10 including the RF receiver 700, the controller 370is connected to the RF receiver 700 and receives the message signal 702therefrom via message/control line 704. The RF receiver 700 alsoreceives the logic signal 362 from the covert logic device 360 and isconfigured to synchronize the A/D converter 350 with the data processor400 for subsequent generation of the digital signal 372 in response tothe message signal 702 and the logic signal 362.

For embodiments of the bio-sensor system 10 including the plurality ofsensors 210, the A/D assembly 300 further includes the switch 310 whichis connected to the controller 370 via sensor selection line 314. Theswitch 310 is also connected the processor filter 320 via switch signalline 312. In such embodiments, the controller 370 is responsive to themessage signal 702 and is operative to cause the switch 310 to selectamong a plurality of sensor signals 234 for subsequent transmissionthereof to the processor filter 320. As was earlier mentioned, in suchconfigurations of the bio-sensor system 10 having multiple ones of thesensors 210, the data processor 400 may be configured to assign a presetidentification code to the digital signal 372 for identifying the sensor210 from which the sensor signal 234 originates. The digital signal 372may be either a packet of serial data (i.e., a burst of data over afixed duration) or a stream of data that lasts as long as information isrequested by the remote transponder 800 depending on the contents of themessage signal 702 transmitted to the controller 370 via themessage/control line 704.

Referring now to FIG. 3, the specific architecture of the data processor400 will be described in detail. In general, the data processor 400receives the digital signal 372 from the A/D assembly 300 and filters,amplifies and/or encodes the digital signal 372 to generate a processeddata signal 462. Power to the data processor 400 is supplied via powerline 606 to the program counter 430. If included, the RF receiver 700transmits the message signal 702 to the program counter 430 viamessage/control line 706 to control and synchronize telemetryoperations. The data processor 400 may be configured to gate the datasignal 462 to determine when to transmit the data signal 462 to theremote transponder 800. In addition, the data processor 400 may also beconfigured to sum the data signal 462 with other data (i.e., from othersensors 210). As can be seen in FIG. 3, the data processor 400 includesa signal filter 410, an amplifier 420, a program counter 430, aninterrupt request device 442, a calculator 450 and a digital filter 460.The signal filter 410 is connected to the A/D assembly 300 and isconfigured to receive the digital signal 372 and remove unwanted noiseor aliasing components that may be included as a result of conversion ofthe sensor signal 234 from analog to digital. The signal filter 410ultimately generates a filtered signal 412. The filtered signal 412 isin digital format and is made up of a series of high and low voltages.

Still referring to FIG. 3, the amplifier 420 is connected to the signalfilter 410 and is configured to receive the filtered signal 412therefrom and generate an amplified signal 422 in response thereto. Theamplifier 420 isolates the data processor 400 from the analog-to-digitalconversion process and prepares the voltage level for a calculationstage. As was earlier mentioned, the program counter 430 is connected tothe RF receiver 700 and the power receiver 600 and is configured toreceive respective ones of the message signal 702 and the power signal602. The program counter 430 also generates a gated signal 432. Theinterrupt request device 442 is connected to the program counter 430 andis configured to receive the gated signal 432 and generate an interruptrequest signal 442.

The calculator 450 is connected to the amplifier 420 and the interruptrequest device 442 and is configured to receive respective ones of thefiltered signal 412, the amplified signal 422 and the gated signal 432and generate an encoded signal 452. In this regard, the program counter430, interrupt request device 442 and calculator 450 cooperate togetherin order to gate (i.e., start and stop) the signal and may additionallyassign a unique message identification code (e.g., to identify theparticular sensor(s) 210 from which the signal originated). In addition,error detection and prevention bits may be added to increase reliabilityand integrity of the signal by repeating a portion or all of the messagein the same data packet. The digital filter 460 is connected to thecalculator 450 and is configured to receive the encoded signal 452therefrom and generate the data signal 462. The digital filter 460shapes the series of high and low voltages that make up the digitalsignal 372 for subsequent modulation by the RF transmitter 500.

Referring now to FIG. 4, the architecture of the RF transmitter 500 willbe described in detail. In general, the RF transmitter 500 modulates thedata signal 462 onto a radio carrier of a desired frequency, amplifiesthe modulated carrier and sends it to an RF transmitter antenna 501 forradiation to the remote transponder 800. Shown in FIG. 4 aresubcomponents of the RF transmitter 500 comprising a data input filter570, a modulator 580, a first transmitter amplifier 530, a transmitterfilter 540, a second transmitter amplifier 520, a surface acoustic wave(SAW) filter 510 and the RF transmitter antenna 501. The RF transmitter500 is powered upon receiving the power signal 602 at the modulator 580from the power receiver 600 via power line 608. If the bio-sensorincludes the RF receiver 700, the message signal 702 is also receivedtherefrom at the modulator 580 via message/control line 708. The datainput filter 570 is connected to the data processor 400 and isconfigured to receive the data signal 462 therefrom to filter outhigh-frequency spectral components and generate a filtered data signal585 in response thereto.

Referring still to FIG. 4, the modulator 580 is connected to the powerreceiver 600, the RF receiver 700 and the data input filter 570 and isconfigured to pulse code modulate the filtered data signal 585 byvarying an amplitude thereof and generating a first and second modulatedsignal 583, 586 in response thereto. The first transmitter amplifier 530is connected to the modulator 580 and is configured to receive the firstmodulated signal 583 therefrom. The transmitter filter 540 generates afeedback signal 532 which is received by the first transmitter amplifier530. The transmitter filter 540 cooperates with the first transmitteramplifier 530 to create a first amplified signal 522 at the desiredfrequency of radio transmission. The second transmitter amplifier 520 isconnected to the modulator 580 and the first transmitter amplifier 530and is configured to receive respective ones of the second modulatedsignal 586 and the first amplified signal 522 therefrom and generate asecond amplified signal 512 having a desired power level that ispreferably sufficient for reliable transmission to the remotetransponder 800.

As shown in FIG. 4, the modulator 580 also receives input from enablecontrol 582 input and modulation control 584 input to aid in performingthe modulation function. The modulator 580 impresses (i.e., modulatesvia pulse-code modulation) the processed data in the data signal 462onto the radio carrier via the first and second transmitter amplifiers530, 520. The amplitude of the radio carrier is varied by the first andsecond modulated signals 583, 586. However, other well known modulationmethods may be used to effect different cost, range, data rate, errorrate and frequency bands. The SAW filter 510 is connected to the secondtransmitter amplifier 520 and is configured to receive the secondamplified signal 512 and remove unwanted harmonics that may lie outsidethe allocated frequency spectrum for the type of radio service utilizedby the bio-sensor system 10. The SAW filter 510 generates a transmittedsignal 502 in response to the second amplified signal 512. The RFtransmitter antenna 501 is connected to the SAW filter 510. Thetransmitted signal 502 is passed to the RF transmitter antenna 501 whichis configured to radiate the transmitted signal 502 for receipt by thereceiving antenna 801 of the remote transponder 800.

Referring now to FIG. 6, the circuit architecture of the power receiver600 will be described in detail. As was earlier mentioned, the powerreceiver 600 is configured to collect power from the scanner signal 882.The scanner signal 882 is received at a power receiver antenna 601 (forembodiments lacking the RF receiver 700). The power is delivered to theA/D assembly 300, data processor 400 and RF transmitter 500 via powerlines 604, 606, 608. As shown in FIG. 6, the subcomponents of the powerreceiver 600 include a syntonic oscillator 610, a rectifier 620, afilter 630, a first regulator 650, a second regulator 660 and a sensorreference supply 640. The syntonic oscillator 610 may be connected tothe RF receiver antenna 701 or to the power receiver antenna 601. Thesyntonic oscillator 610 is configured to receive the scanner signal 882(in sinusoidal form) and prepare the scanner signal 882 for conversioninto a direct current (DC) voltage signal 632.

The syntonic oscillator 610 is configured to generate an alternatingcurrent (AC) voltage signal 612 in response to the scanner signal 882.The scanner signal 882 cycles between plus and minus currents and has anaverage current of zero micro-amps. The rectifier 620 is connected tothe syntonic oscillator 610 and is configured to receive the AC voltagesignal 612 therefrom. The rectifier 620 sums positive currents andinverts negative currents by means of diode junctions such that allcurrents are added into one direction. The diodes have a thresholdvoltage that must be overcome and which creates discontinuities incurrent flow. In this manner, the rectifier 620 generates the coursedirect voltage signal 622 that has discontinuities every half cycle.

The filter 630 is connected to the rectifier 620 and is configured toreceive the direct voltage signal 622 therefrom. The filter 630 has acapacitor (not shown) that is configured to store energy from cycles ofthe generally coarse direct voltage signal 622 for release as asubstantially smooth DC voltage signal 632. As was earlier mentioned,the voltage level is dependent on proximity of the remote transponder800 and is preferably greater than that which is required to power theon-chip transponder 100. The first regulator 650 is connected to thefilter 630 and is configured to receive the DC voltage signal 632therefrom and generate a first voltage signal 652 to power the A/Dassembly 300, the data processor 400 and the RF transmitter 500.

The second regulator 660 is connected to the filter 630 and isconfigured to receive the DC voltage signal 632 therefrom and generate asecond voltage signal 662 to power the A/D assembly 300, the dataprocessor 400 and the RF transmitter 500. The first and secondregulators 650, 660 create the smooth first and second voltage signals652, 662 to form the power signal 602 at a specific voltage level asrequired by the on-chip transponder 100, independent of proximity of theremote transponder 800 to the on-chip transponder 100. Power signal 602is delivered to the A/D assembly 300, the data processor 400 and the RFtransmitter 500 via power lines 604, 606, 608. The sensor referencesupply 640 is connected to the filter 630 and is configured to receivethe DC voltage signal 632 therefrom and generate a sensor referencevoltage signal 642 to supply power to the sensor assembly 200.

Referring briefly to FIG. 7, shown is a block diagram of the RF receiver700 that may be included with the on-chip transponder 100. In general,the RF receiver 700 receives the scanner signal 882, which is decoded bythe RF receiver 700, and alerts the on-chip transponder 100 that arequest for data has been made. The decoded data informs the A/Dassembly 300, the data processor 400 and the RF transmitter 500 as towhich data is to be sent and when to send the data. In general, the RFreceiver 700 reverses all transmitter steps that are performed by the RFtransmitter 500. Subcomponents of the RF receiver 700 include an RFreceiver antenna 701, a SAW filter 710, a first RF amplifier 720, a SAWdelay 730, a second RF amplifier 740, a pulse generator 750 and adetector-filter 790. The RF receiver antenna 701 is configured toreceive the scanner signal 882 from the remote transponder 800. The SAWfilter 710 is connected to the RF receiver antenna 701 and is configuredto receive the scanner signal 882 therefrom and filter the scannersignal 882 of unwanted signals that may overdrive or interfere with theoperation of the RF receiver 700.

The SAW filter 710 generates a filtered scanner signal 712 in responsethereto. The filtered scanner signal 712 may be weak after filtering andis therefore boosted (i.e., amplified) by the first RF amplifier 720 toa level that may be detected by demodulation circuitry. The demodulationcomponentry is comprised of the SAW delay 730, the second RF amplifier740 and the pulse generator 750 connected as shown in FIG. 7. Ingeneral, the demodulating componentry cooperates to recover datacontained in the scanner signal 882. The first RF amplifier 720 isconnected to the SAW filter 710 and is configured to receive thefiltered scanner signal 712 therefrom and generate a first amplified RFsignal 722 in response thereto. The SAW delay 730 is connected to thefirst RF amplifier 720 and is configured to receive the first amplifiedRF signal 722 therefrom and generate a compared signal 732.

The second RF amplifier 740 is connected to the SAW delay 730 and isconfigured to receive the compared signal 732 therefrom. The pulsegenerator 750 is connected in parallel to the SAW delay 730 at the firstand second RF amplifiers 720, 740 and cooperates therewith to generatefirst and second pulse signals 752, 754 for receipt by respective onesof the first and second RF amplifiers 720, 740 such that the second RFamplifier 740 generates a second amplified RF signal 741. Thedetector-filter 790 is connected to the second RF amplifier 740 and isconfigured receive the second amplified RF signal 741 therefrom andextract data from the scanner signal 882 and generate the message signal702. The message signals 702 are passed to telemetry blocks of the A/Dassembly 300, the data processor 400 and the RF transmitter 500 viamessage/control lines 704, 706, 708 to alert the blocks that a sensor210 reading has been requested. The message/control lines 704, 706, 708also convey and transmit/receive coordination and sensor 210 selectionfor configurations where the bio-sensor system 10 includes multiple onesof the sensors 210.

Referring now to FIG. 2, the circuit architecture of the remotetransponder 800 will be described in detail. As shown, the remotetransponder 800 may include transmitting subcomponents for transmittingdata to the on-chip transponder 100 as well as receiving subcomponentsfor receiving the data contained in the data signal 462 which istransmitted by the on-chip transponder 100. The transmittingsubcomponents may comprise an oscillator 860, an encoder 870, a powertransmitter 880 and a transmitting antenna 883. The oscillator 860 isconfigured to generate an analog signal 862 at a predeterminedfrequency. The encoder 870 is connected to the oscillator 860 and isconfigured to receive and modulate the analog signal 862 and generate anencoded signal 872 in response thereto. The power transmitter 880 isconnected to the encoder 870 and is configured to receive and amplifythe encoded signal 872 and generate the scanner signal 882. Thetransmitting antenna 883 is connected to the power transmitter 880 andis configured to receive the scanner signal 882 therefrom for radiotransmission to the on-chip transponder 100.

Referring still to FIG. 2, the remote transponder 800 may also includethe receiving subcomponents to allow receiving of the scanner signal 882from the on-chip transponder 100. The receiving subcomponents of theremote transponder 800 are structurally and functionally equivalent tothe RF receiver 700 as shown in FIG. 7 and as described above. Thereceiving components of the remote transponder 800 may comprise areceiving antenna 801, a SAW filter 810, a first RF amplifier 820, a SAWdelay 830, a second RF amplifier 840, a pulse generator 850 and adetector-filter 890. The receiving antenna 801 is configured to receivethe transmitted signal 502 from the RF transmitter 500. The SAW filter810 is connected to the receiving antenna 801 and is configured toreceive and filter the transmitted signal 502 of unwanted signals thatmay interfere with the remote transponder 800 and generate a filtered RFsignal 812 in response thereto. The first RF amplifier 820 is connectedto the SAW filter 810 and is configured to receive the filtered RFsignal 812 therefrom and generate a first amplified RF signal 822 inresponse thereto.

The SAW delay is connected to the first RF amplifier 820 and isconfigured to receive the first amplified RF signal 822 therefrom andgenerate a compared signal 832. The second RF amplifier is connected tothe SAW delay 830 and is configured to receive the compared signal 832therefrom. The pulse generator is connected in parallel to the SAW delay830 at the first and second RF amplifiers 820, 840 and cooperatestherewith to generate first and second pulse signals 852, 854 forreceipt by respective ones of the first and second RF amplifiers 820,840 such that the second RF amplifier generates 840 a second amplifiedRF signal 841. The detector-filter 890 is connected to the second RFamplifier and is configured receive the second amplified RF signal 841for extraction of digitized data therefrom.

As is also shown in FIG. 2, the bio-sensor system 10 may further includea decoder 900 connected to the detector-filter 890 by data output lines902, 904 and configured to receive the second amplified RF signal 841for extraction of digitized data therefrom. For configurations of thebio-sensor system 10 having the plurality of sensors 210 wherein eachone of the sensor 210 is operative to sense a physiological parameter ofthe patient and generate the sensor signal 234 in response thereto, thedecoder 900 may be configured to select one from among the plurality ofsensor signals 234 from which to receive data.

The decoder 900 may be configured to convert the digitized data back tooriginal physiological data. The decoder 900 may also check the secondamplified RF signal 841 for errors such that an operator may be notifiedwhether or not the telemetry message was successfully received. Thedecoder 900 allows the sensor signal 234 data to be displayed on theremote transponder 800 such as a handheld device. Alternatively, thesensor signal 234 data may be stored in a computer database. Thedatabase may add a time stamp and patient information in order to make acomplete record of the telemetry event. Combined with other records,trends and behavior may be graphed and analyzed.

Referring now to FIGS. 1 and 2, the operation of the bio-sensor system10 will now be generally described. More specifically, the method ofremotely monitoring physiological parameters using the bio-sensor system10 will be described wherein the bio-sensor system 10 broadly comprisesthe remote transponder 800 and the on-chip transponder 100 having thesensor 210 and which is implantable in the patient. The method comprisesthe steps of remotely generating and wirelessly transmitting the scannersignal 882 with the remote transponder 800 wherein the scanner signal882 contains radio signal power and a telemetry data request. Thescanner signal 882 is received at the on-chip transponder 100 whereuponthe scanner signal 882 is filtered, amplified and demodulated togenerate the message signal 702.

Radio signal power is then collected from the scanner signal 882 and thepower signal 602 is generated in response thereto. Simultaneously, uponbeing powered by the sensor reference voltage signal 642, the sensor 210senses at least one physiological parameter of the patient in the manneras was described above and generates the analog sensor signal 234. Thepower signal 602, the analog sensor signal 234 and the message signal702 are all received at the A/D assembly 300 which then generates thedigital signal 372 which is representative of the analog sensor signal.The power signal 602, the message signal 702 and the digital signal 372are then received at the data processor 400 which prepares the digitalsignal 372 for modulation. The data processor 400 then generates thedata signal 462 which is representative of the digital signal 372. Thepower signal 602, the message signal 702 and the data signal 462 arereceived at the RF transmitter 500 which then modulates, amplifies,filters and wirelessly transmits a transmitted signal 502 from theon-chip transponder 100. The remote transponder 800 then received thetransmitted signal 502 from the on-chip transponder 100 and extractsdata that is representative of the physiological parameter of thepatient.

Referring briefly to FIG. 8 a, wherein the sensor 210 is configured asthe 2-pin glucose sensor 210, the method may further comprise steps forenhancing the stability and precision of the power supplied to theelectrode assembly 201 by first tuning the power signal 602 with thefirst precision resistor 224 to generate the sensor reference voltagesignal 642 at the level of about positive 0.7 volts. The sensorreference voltage signal 642 is received at the first operationalamplifier 220 which generates the precision sensor reference voltagesignal 223. The voltmeter 250 monitors the precision sensor referencevoltage signal to establish a sensor 210 operating point. The firstoperational amplifier 220 cooperates with the voltmeter 250 to bufferthe precision sensor reference voltage signal 223 in order to generate asubstantially accurate sensor reference voltage signal 226.

The accurate sensor reference voltage signal 226 is applied to the firstterminal 202 to cause the reaction with the patient's blood which causescurrent to discharge from the second terminal 204 in the manner earlierdescribed. The current discharges at the second terminal 204 inproportion to the glucose level. By tuning the second precision resistor240, which is connected in series to the second operational amplifier230, a voltage divider is formed with the glucose sensor 210. The secondprecision resistor 240, in cooperation with the second operationalamplifier 230, measures the level of discharging current and generatesthe sensor signal 234 which is substantially proportional to the glucoselevel of the patient.

Referring briefly to FIG. 8 b, for the case where the sensor 210 is a3-pin glucose sensor 210 including the third terminal 206 that isco-located with the first and second terminals 204, 206, the method ofsensing the glucose level further comprises the steps of diverting aportion of the current away from the second terminal 204. This isperformed by discharging current at the third terminal 206 duringapplication of the accurate sensor reference voltage signal 226 to thefirst terminal 202. The current from the third terminal 206 is passesthrough the auxiliary control circuit 260 which is connected between thethird electrode and the second operational amplifier 230. The auxiliarycontrol circuit 260 monitors and controls the amount of currentdischarging from the third terminal 206 in order to stabilize theaccurate sensor reference voltage signal 226 applied to the firstterminal 202 which may increase the operational life of the glucosesensor 210.

Additional modifications and improvements of the present invention mayalso be apparent to those of ordinary skill in the art. Thus, theparticular combination of parts described and illustrated herein isintended to represent only certain embodiments of the present invention,and is not intended to serve as limitations of alternative deviceswithin the spirit and scope of the invention.

1. A bio-sensor system adapted to provide a substantially stable voltageto a sensor assembly that is implantable in a patient such thatphysiological parameters thereof may be accurately measured, thebio-sensor system comprising: a remote transponder configured totransmit a scanner signal to the sensor and to receive a data signaltherefrom; an implantable on-chip transponder in wireless communicationwith the remote transponder and being configured to receive the scannersignal and transmit the data signal, the on-chip transponder including:a sensor being configured to generate a sensor signal representative ofthe physiological parameter of the patient; a power receiver configuredto receive the scanner signal from the remote transponder and togenerate a power signal for powering the on-chip transponder; ananalog-to-digital (A/D) assembly connected to the power receiver and thesensor, the A/D assembly being configured to respectively receive thepower signal and the sensor signal and generate a digital signal inresponse thereto; a data processor connected to the A/D assembly and thepower receiver, the data processor being configured to respectivelyreceive, the power signal and the digital signal and generate a datasignal in response thereto; and an RF transmitter connected to the powerreceiver and the data processor and being configured to respectivelyreceive the power signal and the data signal and to modulate, amplify,filter and transmit the data signal; wherein the power receiver isconfigured to supply a substantially non-deviating sensor referencevoltage to the sensor for accurate measurement of the physiologicalparameter, the remote transponder being configured to receive the datasignal from the RF transmitter and to extract data representative of thephysiological parameter.
 2. The bio-sensor system of claim 1 wherein:the sensor is a glucose sensor having an electrode assembly in fluidcommunication with the patient's blood and being configured to measure aglucose level thereof; the sensor reference voltage being supplied tothe electrode assembly at a substantially constant value of aboutpositive 0.7 volts.
 3. The bio-sensor system of claim 2 wherein theglucose sensor is a 2-pin glucose sensor with the electrode assemblyhaving first and second terminals in fluid communication with thepatient's blood, the glucose sensor further including: a first precisionresistor connected to the power receiver and configured to receive thesensor reference voltage therefrom for excitation of the glucose sensor;a first operational amplifier connected to the first precision resistorand being configured to receive the sensor reference voltage therefromand generate a precision sensor reference voltage in response thereto; avoltmeter connected to the first operational amplifier and the firstprecision resistor and being configured to monitor the precision sensorreference voltage and establish a sensor operating point, the firstoperational amplifier and the voltmeter cooperating to buffer theprecision sensor reference voltage and apply a substantially accuratesensor reference voltage to the first terminal; a second operationalamplifier connected to the second terminal and being configured toreceive current discharging therefrom in response to the accurate sensorreference voltage applied to the first terminal; and a tunable secondprecision resistor connected to the second operational amplifier andcooperating therewith to generate a sensor signal that is substantiallyproportional to the glucose level of the patient's blood.
 4. Thebio-sensor system of claim 3 wherein the glucose sensor is a 3-pinglucose sensor with the electrode assembly further including a thirdterminal co-located with the first and second terminals and being influid communication with the patient's blood, the glucose sensor furtherincluding: an auxiliary control circuit connected between the thirdelectrode and the second operational amplifier and being configured tomonitor and control an amount of current discharging from the thirdterminal; wherein the third terminal is configured to divert currentaway from the second electrode during application of the accurate sensorreference voltage applied to the first terminal such that theoperational life of the glucose sensor may be increased.
 5. A bio-sensorsystem adapted to provide a substantially stable voltage to a sensorassembly that is implantable in a patient such that physiologicalparameters thereof may be accurately measured, the bio-sensor systemcomprising: a remote transponder configured to transmit a scanner signalto the sensor and to receive a data signal therefrom; an implantableon-chip transponder in wireless communication with the remotetransponder and being configured to receive the scanner signal andtransmit the data signal, the on-chip transponder including: a sensorbeing configured to generate a sensor signal representative of thephysiological parameter of the patient; a radio frequency (RF) receiverconfigured to receive the scanner signal from the remote transponder andto filter, amplify and demodulate the scanner signal and generate amessage signal for controlling the on-chip transponder; a power receiverconfigured to receive the scanner signal from the remote transponder andto generate a power signal for powering the on-chip transponder; ananalog-to-digital (A/D) assembly connected to the power receiver, the RFreceiver and the sensor, the A/D assembly being configured torespectively receive the power signal, the sensor signal and the messagesignal and generate a digital signal in response thereto; a dataprocessor connected to the A/D assembly, the power receiver and the RFreceiver, the data processor being configured to respectively receivethe power signal, the digital signal and the message signal and generatea data signal in response thereto; and an RF transmitter connected tothe power receiver, the data processor and the RF receiver and beingconfigured to respectively receive the power signal, the data signal andthe message signal and to modulate, amplify, filter and transmit thedata signal; wherein the power receiver is configured to supply asubstantially non-deviating sensor reference voltage to the sensor foraccurate measurement of the physiological parameter, the remotetransponder being configured to receive the data signal from the RFtransmitter and to extract data representative of the physiologicalparameter.
 6. The bio-sensor system of claim 5 wherein: the sensor is aglucose sensor having an electrode assembly in fluid communication withthe patient's blood and being configured to measure a glucose levelthereof; the sensor reference voltage being supplied to the electrodeassembly at a substantially constant value of about positive 0.7 volts.7. The bio-sensor system of claim 6 wherein the glucose sensor is a2-pin glucose sensor with the electrode assembly having first and secondterminals in fluid communication with the patient's blood, the glucosesensor further including: a first precision resistor connected to thepower receiver and configured to receive the sensor reference voltagetherefrom for excitation of the glucose sensor; a first operationalamplifier connected to the first precision resistor and being configuredto receive the sensor reference voltage therefrom and generate aprecision sensor reference voltage in response thereto; a voltmeterconnected to the first operational amplifier and the first precisionresistor and being configured to monitor the precision sensor referencevoltage and establish a sensor operating point, the first operationalamplifier and the voltmeter cooperating to buffer the precision sensorreference voltage and apply a substantially accurate sensor referencevoltage to the first terminal; a second operational amplifier connectedto the second terminal and being configured to receive currentdischarging therefrom in response to the accurate sensor referencevoltage applied to the first terminal; and a tunable second precisionresistor connected to the second operational amplifier and cooperatingtherewith to generate a sensor signal that is substantially proportionalto the glucose level of the patient's blood.
 8. The bio-sensor system ofclaim 7 wherein the glucose sensor is a 3-pin glucose sensor with theelectrode assembly further including a third terminal co-located withthe first and second terminals and being in fluid communication with thepatient's blood, the glucose sensor further including: an auxiliarycontrol circuit connected between the third electrode and the secondoperational amplifier and being configured to monitor and control anamount of current discharging from the third terminal; wherein the thirdterminal is configured to divert current away from the second electrodeduring application of the accurate sensor reference voltage applied tothe first terminal such that the operational life of the glucose sensormay be increased.
 9. The bio-sensor system of claim 5 further includinga plurality of sensors, each one of the sensors being operative to sensea distinct physiological parameter of the patient and generate a sensorsignal representative thereof.
 10. The bio-sensor system of claim 9wherein the RF receiver is configured to coordinate requests for datafrom one or more of the sensors for subsequent transmission of the datato the remote transponder.
 11. The bio-sensor system of claim 10 whereinthe wherein the data processor is configured to assign a presetidentification code to the digital signal for identifying the sensorfrom which the sensor signal originates.
 12. A method of remotelymonitoring physiological parameters using a bio-sensor system comprisinga remote transponder and an on-chip transponder having a sensorimplantable in a patient, the method comprising the steps of: a.remotely generating and wirelessly transmitting a scanner signal withthe remote transponder, the scanner signal containing radio signal powerand a telemetry data request; b. receiving the scanner signal at theon-chip transponder and filtering, amplifying and demodulating thescanner signal to generate a message signal in response thereto; c.collecting the radio signal power from the scanner signal and generatinga power signal in response thereto; d. sensing at least onephysiological parameter of the patient at the sensor and generating ananalog sensor signal in response thereto; e. receiving the power signal,the analog sensor signal and the message signal at an analog-to-digital(A/D) assembly and generating a digital signal representative of theanalog sensor signal; f. receiving the power signal, the message signaland the digital signal at a data processor and preparing the digitalsignal for modulation and generating a data signal representative of thedigital signal; g. receiving the power signal, the message signal andthe data signal at an RF transmitter and modulating, amplifying,filtering and wirelessly transmitting the data signal; and h. receivingthe data signal at the remote transponder and extracting datarepresentative of the physiological parameter of the patient.
 13. Themethod of claim 12 wherein the sensor is a 2-pin glucose sensor havingan electrode assembly with first and second terminals in fluidcommunication with the patient's blood for sensing a glucose level ofthe patient, step (d) further comprising the steps of: tuning the powersignal with a first precision resistor to generate a sensor referencevoltage of about positive 0.7 volts for excitation of the glucosesensor; receiving the sensor reference voltage at a first operationalamplifier and generating a precision sensor reference voltage;monitoring the precision sensor reference voltage with a voltmeterconnected to the first operational amplifier and the first precisionresistor to establish a sensor operating point; buffering the precisionsensor reference voltage with the first operational amplifier incooperation with the voltmeter to generate a substantially accuratesensor reference voltage; applying the substantially accurate sensorreference voltage to the first terminal to cause current to dischargefrom the second terminal in response to a reaction with the patient'sblood at the first and second terminals; receiving the dischargingcurrent at a second operational amplifier, the current beingproportional to the glucose level of the patient's blood; and tuning asecond precision resistor connected to the second operational amplifierto form a voltage divider with the glucose sensor; measuring thedischarging current with the second precision resistor in cooperationwith the second operational amplifier; and generating the sensor signalthat is substantially proportional to the glucose level.
 14. The methodof claim 13 wherein the sensor is a 3-pin glucose sensor additionallyincluding a third terminal co-located with the first and secondterminals and being in fluid communication with the patient's blood,step (d) further comprising the steps of: diverting a portion of thecurrent away from the second terminal by discharging current at thethird terminal during application of the substantially accurate sensorreference voltage to the first terminal; receiving the dischargingcurrent at an auxiliary control circuit connected between the thirdelectrode and the second operational amplifier; and monitoring andcontrolling an amount of current discharging from the third terminal inorder to stabilize the substantially accurate sensor reference voltageapplied to the first terminal and increase the operational life of theglucose sensor